This invention relates generally to improvements in caster wheel assemblies of the type used with wheelchairs and other castered devices. More particularly, this invention relates to an improved caster wheel assembly having adjustable bearing means for variably resisting caster wheel swivel to prevent undesired flutter or shimmy.
Caster wheel assemblies in general are well known in the art for use with many different types of rolling devices. As one example, such caster wheel assemblies are commonly employed as the front wheels in a typical wheelchair. Each caster wheel assembly typically includes a wheel fork unit which rotatably supports a relatively small diameter caster wheel, and which further includes a generally upright swivel post captured by appropriate bearings for rotation about a swivel axis within a fixed cylindrical housing. The fixed housing is adapted in turn for mounting onto frame components of the wheelchair or other castered device. Such caster wheel assemblies beneficially provide a high degree of turning maneuverability.
One major problem encountered with conventional caster wheel assemblies relates to uncontrolled vibrational shimmy or flutter of the caster wheel during rolling movement of the castered device. More specifically, uneven wheel wear and/or nonuniform loading of the castered device can cause one or more caster wheels to experience rapid oscillatory rotation or flutter about the swivel axis. Such oscillatory flutter results in noisy caster wheel operation and imparts a vibrational shimmy to the frame of the castered vehicle. Moreover, during caster wheel flutter, increased effort is normally required to move the castered vehicle. These factors are particularly disadvantageous in a wheelchair environment since they result in a noisy and uncomfortable chair ride, and further require increased manual effort or increased power consumption to drive the wheelchair.
In the past, a variety of caster wheel assemblies have been designed with additional components intended to resist swivel rotation, and thereby resist undesired flutter during operation. In general terms, such antiflutter devices have utilized springs or other resilient structures for physically resisting caster wheel swivel. See, for example, U.S. Pat. Nos. 3,924,292; 4,097,954; 2,963,732 and 4,280,246. Other caster arrangements have included hydraulic components for resisting caster wheel swivel. See, for example, U.S. Pat. No. 4,432,116. However, these swivel resistance arrangements inherently require increased manual or power drive input to move the caster device through turning maneuvers, wherein this increased power requirment can be particularly undesirable in some environments, such as a wheelchair environment. Relatively simple means for variably adjusting the swivel resistance to a minimum force sufficient to prevent caster flutter have not been provided.
There exists, therefore, a significant need for improvements in caster wheel assemblies, particularly with respect to providing adjustable means for variably resisting caster wheel swivel, thereby preventing undesired caster flutter with a minimum force to minimize the power input needed to operate the castered device. The present invention fulfills these needs and provides further related advantages.